Lighting systems for indicating navigational orientation of sea vessels and aircraft are generally known in the art. In regard to fixed-wing aircraft, the lighting systems include red and green position lights attached to the wing tips. Such lighting systems allow observers to determine whether an aircraft is headed towards or away from them, by observing the relative position of the red and green lights. Rotary wing aircraft such as helicopters and gyrocopters provide no fixed surfaces on the port and starboard sides of the aircraft. To date, the problems associated with the lighting systems have been approached by affixing the position of the red and green lights to the port and starboard sides of the aircraft fuselage. However, this provides relatively low geometric separation between the lights, making it more difficult to identify the orientation of the aircraft. Furthermore the aircraft's fuselage tends to restrict the range of relative azimuths over which both red and green lights can be seen simultaneously.
Navigational lighting systems have been proposed for helicopters in which the lights are affixed to the tips of the rotating blades, emitting red and green light in alternation over appropriate angles of revolution to provide the observer with the perception of steady red and green lights on the port and starboard edges of the rotor disk, and optionally a white light on the forward and aft edges of the disk. Such systems require means to control the lights to ensure that they are properly timed with respect to the rotation of the blades. According to U.S. Pat. No. 2,423,528 to Stewart, the lights are controlled via an electric slip ring that also provides the power to the lights. Such slip rings are unreliable, especially in wet weather, and add to the maintenance burden. According to U.S. Pat. No. 3,174,552 to Soucy, the lights are switched by remote control via a wireless transmitter in the fuselage and receivers at the blade tips with no disclosure of means for timing operation of the lights. According to U.S. Pat. No. 3,701,498 to Ferrar and U.S. Pat. No. 3,723,722 to Iderstine et al., optical slip rings with the light are carried to the blade tips via fiber optics. As with the electrical slip ring, such system requires maintenance to keep the optical slip ring surfaces clean and polished.
It is therefore an object of the present invention to provide a navigational indicating system for rotary wing aircraft having means for controlling the blade tip lights that overcome the aforementioned difficulties. It is a further object of the present invention to provide a blade tip lighting system that requires low power and is resistant to damage due to mechanical vibration.
The latter referred relevant prior art is disclosed for example in documents accompanying the filing of the present application.